Digital networks generally involve the modulation of a bit stream on a transmitted signal. While providing for increased efficiencies, digital networks remain susceptible to noise, such as noise from buildings, trees, cars, electrical sources, magnetic sources, and the like. Typically, digital messages are encoded prior to modulation and transmission, and decoded upon reception and de-modulation. The encoded digital messages are generally grouped into one or more bits forming a symbol. The symbol is used to select a high frequency sinusoidal electromagnetic (EM) wave that has been identified as representing the symbol. The technique generally used to transmit a symbol by a high frequency sinusoidal wave is to alter the wave's amplitude, frequency, and/or phase in a designated manner. Therefore, a wave comprising of a predetermined amplitude, frequency, and/or phase represents a symbol, i.e., a predetermined bit pattern.
By transmitting digital messages in such a manner, it is possible to recover from some errors caused by noise in the transmission. The recovery of errors, however, is dependent upon an essentially random distribution of zeros and ones. Unfortunately, if a message comprises a substantial number of zeros, encoders and decoders generally provide poor results. Furthermore, a sequence of the same symbols in the transmission may fail other error correcting function loops, such as a synchronization loop, an auto-gain control loop, and the like, since the function loops may need the differential information of the previously and the next received symbols to function properly.
Therefore, there is a need for a method and an apparatus for transmitting a digital message comprising a substantial number of zeros.